What Causes Unusual Purplish Discharge And Amenorrhea After Unprotected Intercourse?

Hi..I am 19 years old...I am having a brownish purplish discharge...i thought it was just normal spotting....but i have had regular spotting before and it wasn't like this at all. I haven't had my period in almost 3 months...the last time i had it was November 13th. I was wondering if it could be a sign of pregnancy. I ahve been having unprotected sex with my fiance' and I don't know if its something wrong with me or due to a pregnancy.